Fuse medium



May 17 {1927. 1,629,266

F. A. FELDKAMP FUSE MEDIUM Filed April 4, 1923 IN VEN TOR.

Patented may 17, 1927.,

are rates FREDERICK A. FELDKAMP, OF NEWARK, NEW JERSEY, ASSIGNQR, BYMESH E ASSIGN- MEETS, TO ECONOMY FUSE 8; MANUFACTURING -COMPANY, 'ACORPORATIQN 01* NEW roast.

Application filed April 4,

llhis invention relates to improvements in electrical fuse mediums; andthe invention has reference, more particularly, to further improvementsin fuse mediums of 5 the general kind or type disclosed in my priorUnited States Letters Patent No. 1, 473,284, dated Nov. 6th, less.

In said above referred to patent, ll described a fuse element consistingof a main 10 body of high conductivity but also of high melting point(e. g. copper), surrounded at intervals by portions of, another fusiblemetal or metallic alloy possessing a comparatively low melting point (e.g. cadmium, tin, antimony or other suitable easily.

fusible metal or alloys thereof), the latter being adapted under heat toform with the main body a new alloy at comparatively low temperatureeffecting a lowering of the melting point of the main body, whereby thelatter would blow at a considerably lower temperature than would be thecase if its normal comparatively high melting point was maintained.Experience has shown that this type or kind of fuse medium workssatisfactorily in all sizes, provided the quantity of the applied easilyfusible metal or metallic alloy is in proper proportion to the mass ofmain fuse body to'be acted upon. All fuse elements of this type or kindpossees a very pronounced ability to sustain considerable overloadswithout blowing within an undesirable time limit, and at the same timethey respond well to the rules, regulations and requirements of theBoard of Fire Underwriters. While fuse elements of this kind under a onehundred and ten percent load are permitted a temperature rise, underunderwriters rules .not to exceed 70 degrees 0., above a normaltemperature of 24 degrees (1, it is nevertheless desirable to dimensionthe fuse elementfor as low a temperature rise as possible; andruseivinnrn'rir.

1923. Serial No. 629,808.

under a fifty per cent overload. Since, however, the required maximumtime for blowing is fixed by the regulation of the Board of F ireUnderwriters, it might occur that an otherwise excellent fuse,possessing a maximum desired cross-sectional area, would be likely toexceed the allowed maximum time limit for blowing under fifty per centoverloads; and if the apparent remedy of decreasing the cross sectionalarea of the main body or high conductive member of the fuse wasemployed, the result would be a return to a higher and quickertemperature rise to blowing point, and a' consequent lowering ofthedesired overload capacity. Another factor which militates againstincreasing the cross sectional area,

of the single main body or high conductive member of composite fusemediums of the kind herein considered is the fact that if such increaseis made, the active or easily.

fusible metal or metallic alloy must penetrate the main body or highconductive member for a greater distance in order to produce theresultant alloy of lower melting point, which is again a time consumingfactor.

It is the object of this invention therefore to provide a composite fusemedium, of the general kind above discussed, which will permit of aconsiderable variation in the rating thereof, while permitting theemployment of a maximum cross sectional area in the main high conductivemember thereof, without delaying the blowing time beyond the time limitallowed under a fifty per cent overload. In attaining this object I havediscovered that a very efiicicnt main body or high conductive member ofmaxi-. mum cross sectional area is provided by a plurality of unitwiresor strands (e. g. of

copper, brass or combinations thereof) of individually comparativelysmall diameters (e. g. .006 of an inch more or less), which may betwisted together or held together in substantially parallel longitudinalrelation by a binding wire engaged around the same. The main body orhigh conductive member thus formed is coated-with the easily fusiblemetal or metallic alloy (e. g. cadmium, tin, antimony or alloysthereof), such coating penetrating the interstices intermediate thewires or strands so as to intimately unite with the surfaces thereof,

and to be thus so related to the latter as to combine therewith underheat, to form the resultant alloy of lower melting point, and to thuspermit a comparatively low blowing temperature to be effective upon thefuse element in operation. Another advantage of my improved fuseelement, employing a main element comprising a plurality of fine wiresor strands as compared with a solid integral main element ofcomparatively large cross-sectional diameter, is that the appliedcoatingof low melt-ing point metal when applied to the latter type ofmain element tends to produce a quantity ratiobetween high melting pointmetal and low melting point metal which is too low as to the latter, andconsequently is unfavorable in obtaining the alloying action desired,whereas when theformer type of main element consisting of the pluralityof fine wires or strands are bulked together and each of which is coatedby said low melting point metal, to say nothing of the additional amountof the latter metal filling the interstices therebetween, it followsthat the quantity ratio between the high melting point metal and the lowmelting point metal is increased as to the latter, and therefore a moreeflicient and uniform alloying action is obtained.

Another advantage of the novel fuse element, in which the main elementof high melting point metal consists of a'plurality of fine wires orstrands, is that the rating or amperage thereof may be easily varied asdesired by merely reducing or increasing the number of such wires orstrands employed, or by increasing or decreasing within reasonablelimits the size of the base wire. For example, a base wire (i. e. a wireof selected gauge or cross-sectional diameter) may be employed for alltypes and sizes of fuses, the variation of rating or amperage beingobtained by using a greater or lesser number of the same in making upthe main element of the fuse; or a base wire of one gauge or crosssectional diameter may be used in plurality to make up one rating oramperage and another base wire of greater or lesser gauge or crosssectional diameter may be used in plurality to produce another rating oramperage; in either case, however, always employing a plurality ofcomparatively fine wires or strands.

Referring now to the accompanying drawings, the novel fuse element madeaccording to and embodying the principles of the present invention isclearly illustrated therein. In said drawings, Figure 1 is a sideelevation of the complete composite fuse element ready for use; Figure 2is a similar view drawn on an enlarged scale, but with portions shownbroken away to illustrate the different elements of the composite fuseand the manner of assembling the same together;

Figure 3 is a cross section, taken on line 3--3 in said Figure .2, butdrawn on an enlarged scale; and Figure 4 is another cross section, takenon line 4-4 in said Figure 2, and also drawn on an enlarged scale.

Similar characters of reference are employed in allof the abovedescribed views,

to indicate corresponding parts.

Referring now to the drawings, the reference character 5 indicates thecomplete composite fuse made according to and embodying the principlesof this invention. Said novel composite fuse comprises a main elementconsisting'of a plurality of comparatively fine metallic wires orstrands 6, which are of a metal possessing high specific conductivitybut of comparatively high melting point; metals such as copper, brass orcombinations thereof serve the purpose effectively. Said wires orstrands 6 are bunched together so as'to group themselves longitudinally,and the same may be held together in such grouped relation by twistingthe same together, or by binding the same together by convolving one ofthe group about the rest, in the manner illustrated by the convolvedwire 6 in Figure 2. After the plurality of wires or strands 6 are thusgrouped together, the same are dipped or otherwise coated with a mass oflow melting point metal 7 having the property of readily alloying withthe copper or brass wires or strands 6 and 6 of the main element atcomparatively low temperatures when intimately united with the surfacesof the latter; low melting point metals such as cadmium, tin, antimonyor alloys thereof will serve the purpose effectively.

It will be observed that the coating of low melting point metal 7 willnot only penetrate the interstices of the group of wires or strands 6 soas to coat and unite with the surfaces of the individual wires orstrands, but will also fill such interstices so as to produce acomparatively larger quantity ratio between the lowmelting point andhigh melting point metals than is practical to produce by coating asingle wire of the latter metal with the former metal.

When the binding Wire or strand 6 is employed, the spaced convolutionsthereof surrounding the outer surfaces of the grou of wires or strands 6form pockets, whic tend to hold the low meltin point metal by surfacetension, when the latter metal is fiuxed during the operation of thefuse, and consegpently the risk of losing the alloying e ect of the lowmelting point metal by the dropping away of fluxed portions thereof ispractically eliminated.

The composite fuse made according to this invention operatessubstantially in the same manner as set forth in connection with thegeneric type of fus described in my above mentioned prior LettersPatent, and produces a time 1a fuse possessing all the advantages of saigeneric type of fuse, with the additional advantages that the rating andamperage of the same may be easily varied when making up the same.

Other advantages incident to the construction ofcomposite fuse madeaccording to the present invention are that the necessity of providingmany difl'erent sizes of drawing dies for drawing different sizes ofsingle main wire elements to correspond to the various ratings oramperages required is.

abolished, since the number of such dies required may be reduced tocorrespond to the base Wire or wires employed; and, furthermore, theconstruction of the main element in the form of a plurality of wires orstrands permits of passing the element through molten low melting pointmetal by practically a dipping method, thus saving considerable time andlabor, while nevertheless producing a very uniform product easily cutinto desired lengths required for individual fuses; all of whichadvantages tend to permit the most eflicient production methods whenmanufacturing the fuses in quantity.

I claim An electric fuse medium comprising a main element consisting ofa pl'ur'alit of comparatively fine metallic wires of igh specificconductivity and comparatively high melting point disposed inlongitudinally grouped arrangement, said main element having inenveloping relationship therewith a body of metallic material whichunder normal temperature is inactive and under higher temperaturecombines with the metal of said wires toform therewith an alloy of lowermelting point, said wires bein arranged to form pockets for said b0 yofmetallic material, whereby the net effect of surface tension underconditions of fusion is relatively great, said coating being sointimately associated with said fine metallic wires that upon theattainment of said higher temperature a comparatively high proportion ofsaid enveloping metal combines with said metallic wires to form saidalloy.

In testimony, that I claim the invention set forth above I have hereuntoset my hand this 29th day of March, 1923.

FREDERICK A. FELDKAMP.

